Opto-electronic modulator utilizing one or more heating elements

ABSTRACT

Described herein are methods, systems, and apparatuses to utilize an electro-optic modulator including one or more heating elements. The modulator can utilize one or more heating elements to control an absorption or phase shift of the modulated optical signal. At least the active region of the modulator and the one or more heating elements of the modulator are included in a thermal isolation region comprising a low thermal conductivity to thermally isolate the active region and the one or more heating elements from a substrate of the PIC.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/612,316, filed Feb. 3, 2015, which claims priority to U.S.Provisional Patent Application Ser. No. 61/936,192, filed Feb. 5, 2014,each of which are incorporated herein by reference in their entirety.

FIELD

Embodiments generally pertain to optical devices and more specificallyto modulators included in photonic integrated circuits.

BACKGROUND

Photonic Integrated Circuits (PICs) include interconnected semiconductoroptical devices that are co-located on a single chip. Optical devices ona PIC have a variety of functionalities. For example, one optical device(e.g., a modulator) may modulate optical signals, while another opticaldevice (e.g., a laser) may generate optical signals. Optical deviceshave thermal operating conditions dependent on their function, and thusreact differently to changes in device operating temperature. Forexample, one optical device may need to dissipate heat, and anotheroptical device may need to retain heat or dissipate less heat in orderto operate as expected. Furthermore, due to the close proximity ofoptical devices on a PIC, the thermal performance of one device mayimpact the performance of other devices on the PIC.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description includes discussions of figures havingillustrations given by way of example of implementations and embodimentsof the subject matter disclosed herein. The drawings should beunderstood by way of example, and not by way of limitation. As usedherein, references to one or more “embodiments” are to be understood asdescribing a particular feature, structure, or characteristic includedin at least one implementation of the disclosure. Thus, phrases such as“in one embodiment” or “in an alternate embodiment” appearing hereindescribe various embodiments and implementations of the disclosure, anddo not necessarily all refer to the same embodiment. However, suchphrases are also not necessarily mutually exclusive.

FIG. 1A is an illustration of an optical modulator utilizing a heatingelement according to an embodiment of the disclosure.

FIG. 1B illustrates a heating element utilized by a plurality of opticalmodulators according to an embodiment of the disclosure.

FIG. 2 is an illustration of an optical modulator utilizing a pluralityof heating elements according to an embodiment of the disclosure.

FIG. 3 is an illustration of an optical modulator utilizing atermination resistor as a heating element according to an embodiment ofthe disclosure.

FIG. 4 is a flow diagram for controlling the operating temperature of anoptical modulator using one or more heating elements according to anembodiment of the disclosure.

FIG. 5A-FIG. 5D illustrate various operating parameters for an opticalmodulator using one or more heating elements according to embodiments ofthe disclosure.

FIG. 6 is an illustration of components of a device or system includinga photonic integrated circuit that further includes at least one opticalmodulator according to an embodiment of the disclosure.

Descriptions of certain details and implementations follow, including adescription of the figures, which may depict some or all of theembodiments described below, as well as a description of other potentialembodiments or implementations of the concepts presented herein. Anoverview of embodiments is provided below, followed by a more detaileddescription with reference to the drawings.

DESCRIPTION

Embodiments of the disclosure describe opto-electronic modulatorsutilizing one or more heating elements. Throughout this specification,several terms of art are used. These terms are to take on their ordinarymeaning in the art from which they come, unless specifically definedherein or unless the context of their use would clearly suggestotherwise. In the following description, numerous specific details areset forth to provide a thorough understanding of the embodiments. Oneskilled in the relevant art will recognize, however, that the techniquesdescribed herein can be practiced without one or more of the specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures, materials, or operations are not shownor described in detail to avoid obscuring certain aspects of thedisclosure.

FIG. 1A is an illustration of an optical modulator utilizing a heatingelement according to an embodiment of the disclosure. In thisembodiment, a modulator 100 is shown to include an input/output (I/O)waveguide 102 and an active region 104. The modulator 100 can beincluded in a photonic integrated circuit (PIC), and the I/O waveguide102 can receive/output an optical signal from/to other components of thePIC, from/to an optical coupler coupled to the PIC, etc.

The I/O waveguide 102 and the active region 104 can comprise the samesemiconductor material, or can comprise different semiconductor material(e.g., heterogeneous silicon/non-silicon material). For example, in someembodiments, the I/O waveguide 102 comprises a silicon waveguide thatcouples light to/from the active region 104, which can be disposed onthe I/O waveguide 102 and can comprise non-silicon material (e.g., III-Vsemiconductor material).

An electric field can be applied to electrical contacts (not shown) ofthe modulator 100 to change the refractive index of the active region104 in order to modulate a received optical signal. Changing therefractive index may include changing the absorption coefficient. Insome embodiments, the modulator 100 can comprise an electro-absorptionmodulator (EAM) to change the power of the received optical signal, oran electro-optical modulator (EOM) to change the phase of the receivedoptical signal.

In many applications for optical transmitters, EAMs may be used tomodulate an optical signal in the on-off-keying (OOK) format. Thesystems in which these transmitters are implanted can operate over awide temperature range. Prior art solutions hold the optical transmitterat a single temperature by means of a thermoelectric cooler (TEC);however, these prior art solutions utilize hermetic structures to sealthe optical transmitter, which can further utilize expensive packagingmaterials and methods. Furthermore, TECs can consume large amounts ofpower.

To reduce the cost and power consumption of optical transmitters,packaging techniques and temperature ranges of operation are utilized sothat the transmitter operates in conditions that match that of theelectrical system surrounding the transmitter. In this scenario, thetransmitter is termed “uncooled;” however, uncooled modulators aresensitive to temperature changes due to the inherent shift of theband-edge in semiconductor absorption above the band gap viaelectron-hole pair creation. In other words, as temperature increases inthe active region 104, the band-edge can shift to longer wavelengths,resulting in higher absorption at a particular wavelength of operation.During operation, this is manifested as an increase in insertion lossand a change in extinction ratio (ER) of the modulator 100. Duringoperation over a wide temperature range, this shift could induce aninsertion loss and ER change that is unacceptable for the system. For anEOM, the most efficient phase shift can occur at a particular offsetbetween the wavelength of the bandgap absorption edge and the wavelengthof the modulated light. As temperature increases in the active region,in addition to increasing the insertion loss of modulator 100, theefficiency of phase shift in an EOM may be reduced.

Embodiments of the disclosure allow a modulator in an uncooled opticaltransmitter to meet the temperature range and wavelength range demandsof a system while relaxing the bias voltage range and maximum biasvoltage, and without consuming large amounts of power. In thisembodiment, a heating element 106 is disposed along (in thisillustration, alongside) the active region 104 to control an operatingtemperature of the modulator 100, and thus, to control an absorption(for EAMs) or phase shift (for EOMs) of the modulated optical signal. Inthis embodiment, a heating element 106 is shown to be disposed along thelength/width (i.e., long dimension) of the active region 104 such thatthe region is heated uniformly (or substantially uniformly) along itslength. As described in further detail below, the heating element 106 isutilized to account for some or all of the temperature range ofoperation, and in effect, reduce the local temperature range of themodulator 100. For example, the heating element 106 may be used tostabilize the gain or phase shift of the modulated optical signal (i.e.,gain or phase shift generated by the active region 104) in response to adetected wavelength change in the modulated optical signal.

In this embodiment, the materials and the structure of the modulator 100may be chosen such that the thermal conductivity for a region 110surrounding the heating element 106 and the active region 104 is high,but is also thermally isolated from the ambient temperature surroundingthe region 110 to increase the power efficiency of the heating element106. The region 110 can be thermally isolated from the substrate of thePIC using any solution to vary its thermal conductivity (e.g., differentmaterials, different structural features such as thermal shunts, etc.).In one embodiment, the region 110 can comprise low thermal conductivitybetween the heating element 106 and a heat sink for the PIC (e.g., aheat sink disposed on the substrate of the PIC), high thermalconductivity between the heating element 106 and the active region 104,and low thermal conductivity between the remaining portions of themodulator 100 and the PIC heat sink.

In embodiments wherein the I/O waveguide 102 and the active region 104comprise different semiconductor material (e.g., heterogeneoussilicon/non-silicon material), the I/O waveguide 102 may be doped tocreate a resistor in silicon to function as the heating element 106(but, in contrast to the illustration of FIG. 1, disposed in the siliconsemiconductor material—i.e., underneath the active region 104). Forthese embodiments, the thermal conductivity between the heater 106 andthe active region 104 is very high due to their proximity to oneanother.

In some embodiments, a PIC may include a plurality of modulators; aheating element can be shared by multiple modulators to increase powerefficiency and reduce the number of heating components in the PIC. FIG.1B illustrates a heating element utilized by a plurality of modulatorsaccording to an embodiment of the disclosure. In this embodiment, theheating element 156 is disposed alongside the active region 162 of themodulator 152, and the active region 164 of the modulator 154. Theheating element 156 may be used to affect or control the active regions162 and 164 simultaneously due to the close proximity of the modulators152 and 154 on the PIC. The heating element can affect or control boththe active regions 162 and 164 in a similar manner, for example, tocontrol the band-edge shifts of both active regions similarly, or due tothe likelihood of ambient temperature changes affecting both modulatorsin a similar fashion. The region 160, shown to include the activeregions 162 and 164 and the heating element 156, may be thermallyisolated from a substrate of the PIC, a heat sink disposed on the PIC,and/or other components of the PIC as discussed above. This embodimentmay be utilized for a Mach-Zehnder modulator (MZM) utilizing two phasemodulators in a push-pull configuration. In these embodiments, twoadjacent modulators could have the same operating wavelength. In someconfigurations they would have the same average power dissipation andbias voltage, such that it would be optimal to use the heater to havethe same band-edge shift for both of modulators 152 and 154.

In addition to thermally isolating regions surrounding the heatingelements, the thermal conductivity of a PIC may be designed such thatthe thermal conductivity between the modulators and a heat sink ishighest where the incident light reaches the active regions of themodulators. This can reduce the amount of self-heating that occurs atthe input of a modulator. A possible failure mechanism of a modulator isreaching a critical temperature, so this type of thermal engineering mayincrease the threshold at which this failure mechanism occurs.Furthermore, by designing thermal conductivity to vary along the lengthof an active region, it may be possible to achieve an optimalperformance giving these competing requirements.

Solutions to vary the temperature along the length of an active regioncan also include utilizing multiple heating elements. FIG. 2 is anillustration of an optical modulator utilizing a plurality of heatingelements according to an embodiment of the disclosure. In thisembodiment, a modulator 200 is shown to include an I/O waveguide 202 andan active region 204. In this embodiment, a plurality of heatingelements 206-209 are shown to be disposed alongside the active region204. The heating elements 206-209 may be controlled independently, insub-sets, or collectively. During some operating conditions, thetemperature along the active region 204 may vary and benon-uniform—e.g., non-uniform self-heating along the active region 204may be due to a non-uniform light absorption profile. The heatingelements 206-209 may heat the active region 204 non-uniformly tocounterbalance the self-heating profile, and thus generating a uniformtemperature along the active region 204. For example, the heatingelements 206-209 may each have a varied resistance along the activeregion 204 to produce non-uniform heating (alternatively, a singleheating element such as the heating elements 106 and 156 of FIG. 1A-FIG.1B can have a varied resistance along the element). In otherembodiments, the heating elements 206-209 can be controlled differentlyto generate a specific temperature profile. For example, the activeregion 204 may have its highest operating temperature where the incidentlight from the I/O waveguide 202 reaches the active region, and thus theheating elements 206 and 207 may be operated at a lower temperaturecompared to the heating elements 208 and 209.

FIG. 3 is an illustration of an optical modulator utilizing atermination resistor as a heating element according to an embodiment ofthe disclosure. In this embodiment, a PIC sub-circuit 300 is shown toinclude a modulator 302 (illustrated as a diode) coupled to atermination resistor 304 (i.e., coupled to the electrical contacts ofthe modulator 302). The termination resistor 304 may be included in themodulation signal circuitry to provide the correct impedance for themodulator driver (i.e., impedance matching to maximize the transfer ofpower from a driver circuit to the modulator 302). When the modulationsignal and bias are supplied to the modulator 302 and the terminationresistor 304, the resistor may dissipate power and create heat, therebyheating the active region of the modulator 302. Thus, in thisembodiment, the termination resistor 304 functions as an impedance forthe modulation signal circuitry and as a heating element for themodulator 302; hence no additional control circuitry or control signalsare needed to heat the modulator 302. Since both heating the modulatorand increasing the bias voltage both shift the band edge to a longerwavelength, a single control loop can adjust the bias voltage of themodulator and obtain an additive effect of shifting the band edgethrough these two means.

A very large bias voltage range allows for a modulator to operate over awide temperature range, but also correspondingly increases thecomplexity of the surrounding electronics. By adjusting the localtemperature of the modulator 300 in response to an increase in appliedbias voltage, the bias voltage range can be relaxed, and in particular,the maximum bias voltage can be decreased.

FIG. 4 is a flow diagram for controlling the operating temperature of anoptical modulator using one or more heating elements according to anembodiment of the disclosure. Flow diagrams as illustrated hereinprovide examples of sequences of various process actions. Although theactions are shown in a particular sequence or order, unless otherwisespecified, the order of the actions can be modified. Thus, the describedand illustrated implementations should be understood only as examples.The illustrated actions can be performed in a different order, and someactions can be performed in parallel. Additionally, one or more actionscan be omitted in various embodiments; thus, not all actions arerequired in every implementation. Other process flows are possible.

A process 400 is shown to include executing an operation for receivingan optical signal at an I/O waveguide of a modulator (block 402). Anoperation for applying an electric field to one or more electricalcontacts disposed on an active region of the modulator to modulate thereceived optical signal is executed (block 404). The applied electricfield modulates the received optical signal by changing a refractiveindex or absorption of the active region. As discussed above, in someembodiments, the I/O waveguide and the active region of the modulatorcan comprise the same semiconductor material, or can comprise different(i.e., heterogeneous) material.

An operation is executed to determine the operating conditions of themodulator (block 406). In some embodiments, a change in operatingtemperature may be detected, or a change from the current operatingtemperature may be desired; in other embodiments, a change in thecurrent output wavelength of the modulated optical signal may bedetected, or a change in the current gain or phase of the modulatedoptical signal may be desired. In response to determining the operatingconditions of the modulator, an operation to control one or more heatingelements disposed along the active region in order to control anabsorption or phase shift of the modulated optical signal is executed(block 408). As discussed above, in some embodiments, a single heatingelement may be utilized, while in other embodiments, a plurality ofheating elements may be utilized; furthermore, the heating element(s)may be controlled independently from the active region (e.g., asdiscussed above with reference to FIG. 2), or may be controlledutilizing the same electric field used to control the absorption orphase shift of the active region of the modulator (e.g., as discussedabove with reference to FIG. 3).

FIG. 5A-FIG. 5D illustrate various operating parameters for an opticalmodulator using one or more heating elements according to embodiments ofthe disclosure. FIG. 5A illustrates an exemplary set of operatingparameters including a graph 502 that illustrates changes to a heatingelement temperature in response to ambient temperature changes, a graph504 that illustrates changes to a modulator bias voltage in response toambient temperature changes, and a graph 506 that illustrates changes toa modulator operating temperature in response to ambient temperaturechanges 506.

As shown in this embodiment, one or more heating elements are controlledto heat a modulator to an initial temperature; in response to anincrease in ambient temperature, the one or more heating elements areadjusted to produce lower heat (as shown in the graph 502) to hold themodulator at an (at least substantially) constant temperature (as shownin the graph 506).

Controlling the modulator according to these parameters allows for theoutput of the modulator to remain constant throughout any ambienttemperature change, and thus, allows the bias voltage applied to themodulator to remain (at least substantially) constant (as shown in thegraph 504). A possible failure mechanism of a modulator is reaching acritical temperature, so in this embodiment, once the ambienttemperature exceeds a threshold, the modulator may be presumed to have anon-reliable output. In other words, in this embodiment the one or moreheating elements are controlled to hold the temperature of the modulatorat or near its maximum temperature of operation at all ambienttemperatures. In this case, the bias voltage on the modulator, as shownin the graph 504, is held constant across all ambient temperatures,simplifying the electronics and reducing the maximum bias voltagerequired.

As discussed above, as temperature increases in the active region of themodulator, the band-edge shifts to longer wavelengths, resulting inhigher absorption or phase shift at a particular wavelength ofoperation. During operation, this is manifested as an increase ininsertion loss and a change in ER of the modulator. To prevent thisinsertion loss/change in the ER, the applied bias voltage to themodulator can be adjusted, or the temperature of the modulator can beadjusted, as shown in the exemplary set of operating parametersillustrated in FIG. 5B.

As shown in graph 516, one or more heating elements are controlled toheat a modulator to an initial temperature; in response to an increasein ambient temperature, the one or more heating elements are adjusted toproduce lower heat (as shown in the graph 512) to hold the modulator toat an (at least substantially) constant temperature (as shown in thegraph 516) when the ambient temperature changes within the range oftemperature values “A” to “B.” In other words, in this embodiment theone or more heating elements are utilized when the ambient temperaturedrops below a specific point in the operational temperature range (i.e.,temperature value “B”). In effect, this reduces the total localtemperature range of the modulator, relaxing the bias voltagerequirements and reducing the maximum bias voltage required.

In this embodiment, the one or more heating elements are used over asubset of the operational temperature range of the modulator (i.e., fromthe range of temperature values “A” to “B”); within this temperaturerange, the bias voltage applied to the modulator is constant (as shownin graph 514). The one or more heating elements are disabled when theambient temperature reaches a threshold value (i.e., temperature value“B”) that is less than the modulator's critical temperature. As shown inthe graphs 514 and 516, when the modulator temperature increases pastthe temperature value “B,” the bias voltage decreases corresponding tothe increase of the ambient temperature around the modulator to offsetany absorption or phase shift changes in the output signal.

FIG. 5C illustrates another exemplary set of operating parametersaccording to an embodiment of the disclosure. As shown in graphs 522 and526, one or more heating elements are used to increase or decrease theambient temperature of the modulator in order to account for changes inwavelength in the input optical signal (and thus, the x-axis for thesegraphs and graph 524 is the “wavelength” of the modulated opticalsignal). Thus, in this embodiment, as opposed to holding a modulator toa near-constant temperature, one or more heating elements are used tohold the absorption or phase shift of the modulator constant as inputwavelength is varied (the bias voltage applied to the modulator is heldconstant, as shown in graph 524).

Active regions comprising III-V material may be sensitive to operationalwavelength. For a given III-V material, and at a single temperature,operation at different wavelengths may produce a different insertionloss and ER. To combat insertion loss/ER, different bias voltages can beapplied to a modulator to tailor its insertion loss and ER to itsparticular wavelength; however, in this embodiment, by shifting theband-edge via a local temperature change, a modulator can operate withthe same applied bias voltage (as shown in the graph 524) or a reducedbias range, simplifying the electrical system and relaxing theadjustable bias voltage amount. Another technical effect is that asingle material specification may be used over a wider wavelength rangeby operating devices at different temperatures, potentially reducing thecost or complexity of a wavelength-reconfigurable PIC (or a PIC used inwavelength division multiplexing (WDM) applications).

FIG. 5D illustrates another exemplary set of operating parametersaccording to an embodiment of the disclosure. These operating parameterscorrespond to embodiments wherein one or more heating elements comprisea termination resistor electrically coupled to the electrical contactsof a modulator (e.g., as shown in FIG. 3). In these embodiments, as thetermination resistor also functions as the heating element of themodulator, it is not separately controlled from the bias voltage;however, the termination resistor/heating element reduces the modulatortemperature range to be less than the ambient temperature range. Asshown in the graph 536, in effect, these embodiments reduce the totallocal temperature range of the modulator (as the modulator is alreadyheated to a certain temperature during initial operation due to theapplication of the bias voltage), and also relax the bias voltagerequirements (as shown in the graph 534).

FIG. 6 is an illustration of components of a device or system includinga PIC that further includes at least one optical modulator according toan embodiment of the disclosure. In this embodiment, a device or system600 is shown to include a printed circuit board (PCB) substrate 602, anorganic substrate 604, an application specific integrated circuit (ASIC)606, and a PIC 608, which exchanges light with an optical fiber 612 viaa connector 610. The optical devices of the PIC 608 are controlled, atleast in part, by control circuitry included in the ASIC 606.

Both the ASIC 606 and the PIC 608 are communicatively coupled via theorganic substrate 604. The PCB 608 is coupled to the organic substrate604 via a ball grid array (BGA) interconnect 616, and may be used tointerconnect the organic substrate (and thus, the ASIC 606 and the PIC608) to other components of the device or system 600 not shown—e.g.,interconnection modules, power supplies, etc.

The PIC 608 may be formed of any semiconductor material suitable forphotonic devices and photonic operation, such as silicon based materials(e.g., silicon (Si), silicon nitride (SiN)), non-silicon material suchas III-V material, magneto-optic material, or crystal substratematerial, or a combination of silicon and non-silicon material(alternatively referred to as “heterogeneous material”). The PIC 608 mayinclude one or more optical devices controlled, at least in part, bycontrol circuitry included in the ASIC 606, and may be formed of anysemiconductor material suitable for electronic devices and electronicoperation, such as Si.

The PIC 608 is shown to include a modulator 620, labeled for exemplarypurposes only (the PIC 608 may include more than one modulator). Themodulator 620 may be used to modulate optical signals generated by oneor more transmission components of the PIC, optical signals receivedfrom the fiber 612, etc. The modulator 620 may comprise an EAM or anEOM, and may have an active region comprising any material suitable formodulation. In some embodiments, the material of the active region ofthe modulator 620 is chosen such that the absorption coefficient of saidregion is easily affected by either the Franz-Keldysh effect if saidregion comprises bulk material (e.g., intrinsic Indium Gallium ArsenidePhosphide (i-InGaAsP) or Indium Aluminum Gallium Arsenide (InAlGaAs)) orthe quantum confined stark effect (QCSE) if said region comprisesmultiple quantum wells (MQW).

As discussed above, the modulator 620 can utilize one or more heatingelements to control an absorption or phase shift of the modulatedoptical signal. As discussed above, at least the active region and theone or more heating elements of the modulator 620 are included in athermal isolation region comprising a low thermal conductivity materialthat is less thermally conductive than a substrate of the PIC 608 tothermally isolate the active region and the one or more heating elementsof the modulator 620 from a heat sink disposed on the PIC (not shown)and/or other components of the PIC 608.

Reference throughout the foregoing specification to “one embodiment” or“an embodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present disclosure. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout the specification are not necessarily all referring tothe same embodiment. Furthermore, the particular features, structures,or characteristics can be combined in any suitable manner in one or moreembodiments. In addition, it is to be appreciated that the figuresprovided are for explanation purposes to persons ordinarily skilled inthe art and that the drawings are not necessarily drawn to scale. It isto be understood that the various regions, layers, and structuresrepresented in the figures can vary in size and dimensions.

The above described embodiments can comprise silicon on insulator (SOI)or silicon-based (e.g., silicon nitride (SiN)) devices, or can comprisedevices formed from both silicon and a non-silicon material. Saidnon-silicon material (alternatively referred to as “heterogeneousmaterial”) can comprise one of III-V material, magneto-optic material,or crystal substrate material.

III-V semiconductors have elements that are found in group III and groupV of the periodic table (e.g., Indium Gallium Arsenide Phosphide(InGaAsP), Gallium Indium Arsenide Nitride (GaInAsN)). The carrierdispersion effects of III-V-based materials can be significantly higherthan in silicon-based materials, as electron speed in III-Vsemiconductors is much faster than that in silicon semiconductors. Inaddition, III-V materials have a direct bandgap which enables efficientcreation of light from electrical pumping. Thus, III-V semiconductormaterials enable photonic operations with an increased efficiency oversilicon for both generating light and modulating the refractive index oflight.

Thus, III-V semiconductor materials enable photonic operation with anincreased efficiency at generating light from electricity and convertinglight back into electricity. The low optical loss and high qualityoxides of silicon are thus combined with the electro-optic efficiency ofIII-V semiconductors in heterogeneous optical devices; in someembodiments, said heterogeneous devices utilize low-loss heterogeneousoptical waveguide transitions between the devices' heterogeneous andsilicon-only waveguides.

Magneto-optic materials allow heterogeneous PICs to operate based on themagneto-optic (MO) effect. Such devices can utilize the Faraday effect,in which the magnetic field associated with an electrical signalmodulates an optical beam, offering high bandwidth modulation, androtates the electric field of the optical mode, enabling opticalisolators. Said magneto-optic materials can comprise, for example,materials such as iron, cobalt, or yttrium iron garnet (YIG).

Crystal substrate materials provide heterogeneous PICs with a highelectro-mechanical coupling, linear electro optic coefficient, lowtransmission loss, and stable physical and chemical properties. Saidcrystal substrate materials can comprise, for example, lithium niobate(LiNbO₃) or lithium tantalate (LiTaO₃).

In the foregoing detailed description, the method and apparatus of thepresent subject matter have been described with reference to specificexemplary embodiments thereof. It will, however, be evident that variousmodifications and changes can be made thereto without departing from thebroader spirit and scope of the present disclosed subject matter. Thepresent specification and figures are accordingly to be regarded asillustrative rather than restrictive.

Embodiments of the disclosure describe a modulator included in a PICcomprising an I/O waveguide to receive an optical signal and output amodulated optical signal, an active region disposed on the waveguide tomodulate the received optical signal, one or more electrical contacts toreceive an electric field to change an absorption or phase shift of theactive region, and one or more heating elements disposed along theactive region to control the absorption or phase shift of the modulatedoptical signal, wherein at least the active region and the one or moreheating elements are included in a thermal isolation region comprising alow thermal conductivity to thermally isolate the active region and theone or more heating elements from a substrate of the PIC.

In some embodiments, the PIC is disposed on a heat sink material, andthermal isolation region is to thermally isolate the active region andthe one or more heating elements from the heat sink material. In someembodiments, the one or more heating elements are to stabilize theabsorption or phase shift of the modulated optical signal in response toa detected wavelength change in the received optical signal.

In some embodiments, the modulator comprises at least one of anelectro-absorption modulator (EAM), and wherein the one or more heatingelements disposed along the active region are to control the absorptionof the modulated optical signal, or an electro-optic modulator (EOM),and wherein the one or more heating elements disposed along the activeregion are to control the phase shift of the modulated optical signal.

In some embodiments, the at least one heating element comprises aplurality of heating elements. In some embodiments, the plurality ofheating elements are disposed on a same side of the active region. Insome embodiments, the plurality of heating elements are disposed onopposing sides of the active region. In some embodiments, each of theplurality of heating elements are independently controlled.

In some embodiments, the one or more heating elements comprises atermination resistor coupled to the one or more electrical contacts. Insome embodiments, the one or more heating elements are further disposedalong a second active region of a second modulator of the PIC, and is tocontrol an absorption or phase shift of a second modulated opticalsignal of the second modulator. In some embodiments, the modulator andthe second modulator are included in a push-pull driven MZM.

Embodiments of the disclosure describe a method comprising receiving anoptical signal at a waveguide of a modulator included in a PIC, applyingan electric field to one or more electrical contacts disposed on anactive region of the modulator to modulate the received optical signalby changing an absorption or phase shift of the active region, andcontrolling one or more heating elements disposed along the activeregion to control an absorption or phase shift of the modulated opticalsignal, wherein at least the active region and the one or more heatingelements are included in a thermal isolation region comprising a lowthermal conductivity material to thermally isolate the active region andthe one or more heating elements from a substrate of the PIC.

In some embodiments, controlling the one or more heating elementsdisposed along the active region to control the absorption or phaseshift of the modulated optical signal comprises adjusting the one ormore heating elements to hold a temperature of the active regionsubstantially constant in response to a change in an ambient temperaturesurrounding the PIC. In some embodiments, the one or more heatingelements are disabled in response to ambient temperature surrounding thePIC exceeding a threshold value.

In some embodiments, controlling the one or more heating elementsdisposed along the active region to control the output wavelength of themodulated optical signal comprises changing a temperature of the activeregion to account for changes in wavelength of the received opticalsignal.

In some embodiments, the one or more heating elements comprises aplurality of heating elements. In some embodiments, controlling the oneor more heating elements disposed along the active region to control theabsorption or phase shift of the modulated optical signal comprisescontrolling each of the plurality of heating elements independently. Insome embodiments, controlling the one or more heating elements disposedalong the active region to control the absorption or phase shift of themodulated optical signal comprises controlling each of the plurality ofheating elements via a single control signal.

In some embodiments, the one or more heating elements comprises atermination resistor coupled to the one or more electrical contactsdisposed on the active region of the modulator such that applying theelectric field to one or more electrical contacts further controls theone or more heating elements.

In some embodiments, the one or more heating elements are furtherdisposed along a second active region of a second modulator of the PIC,and the method further comprises controlling the one or more heatingelements to control an absorption or phase shift of a second modulatedoptical signal of the second modulator.

The invention claimed is:
 1. A modulating system, comprising: a firstwaveguide configured to guide light; a first active region through whichat least a portion of the first waveguide extends; a second waveguideconfigured to guide light; a second active region through which at leasta portion of the second waveguide extends; a single heater positionedalongside and between the first and second active regions; controlcircuitry operable to control the heater to selectively heat the firstand second active regions, wherein operatively the heater varies atleast one of: a first refractive index in the first active region, sothat variations in the first refractive index modulate a phase of thelight in the first waveguide and vary an optical path length traversedby the light in the first waveguide, and a first absorption in the firstactive region, so that variations in the first absorption modulate anintensity of the light in the first waveguide, wherein operatively theheater further varies at least one of: a second refractive index in thesecond active region, so that variations in the second refractive indexmodulate a phase of the light in the second waveguide and vary anoptical path length traversed by the light in the second waveguide, anda second absorption in the second active region, so that variations inthe second absorption modulate an intensity of the light in the secondwaveguide; a heat sink configured to dissipate heat from the controlcircuitry; and a thermal isolation region configured to thermallyisolate the first active region, the second active region, and theheater from the heat sink.
 2. The modulating system of claim 1, whereinoperably controlling the heater comprises providing a selectable currentto the heater to set a temperature in the first active region to a firstspecified value and set a temperature in the second active region to asecond specified value.
 3. The modulating system of claim 1, wherein:operatively, the heater varies the first absorption in the first activeregion, so that variations in the first absorption modulate an intensityof the light in the first waveguide; and the modulating system functionsas an electro-absorption modulator.
 4. The modulating system of claim 1,wherein: operatively, the heater varies the first refractive index inthe first active region, so that variations in the first refractiveindex modulate a phase of the light in the first waveguide; the firstactive region and the heater function as at least part of a firstelectro-optic modulator; operatively, the heater varies the secondrefractive index in the second active region, so that variations in thesecond refractive index modulate a phase of the light in the secondwaveguide; the second active region and the heater function as at leastpart of a second electro-optic modulator; and the first and secondelectro-optical modulators are arranged in a push-pull configuration toform a Mach-Zehnder modulator.
 5. The modulating system of claim 1,further comprising a plurality of electrodes configured to produceelectric fields in the first and second active regions, the electricfields being controlled by the control circuitry.
 6. The modulatingsystem of claim 5, wherein the control circuitry is further configuredto provide selectable voltages to the plurality of electrodes.
 7. Themodulating system of claim 6, wherein the control circuitry isconfigured to provide the selectable voltages to the plurality ofelectrodes in response to a detected wavelength change in the lightdirected through the first or second active regions, the selectablevoltages being selected to stabilize a phase or an intensity of thelight directed through the first or second active regions.
 8. A methodfor modulating light, the method comprising: guiding light through afirst active region of a first waveguide and a second active region of asecond waveguide; selectively heating, with a single heater positionedalongside and between the first and second active regions and undercontrol of control circuitry, the first active region to vary at leastone of: a first refractive index in the first active region, so thatvariations in the first refractive index modulate a phase of the lightin the first waveguide and vary an optical path length traversed by thelight in the first waveguide, and a first absorption in the first activeregion, so that variations in the first absorption modulate an intensityof the light in the first waveguide; selectively heating, under controlof the control circuitry, the second active region to vary at least oneof: a second refractive index in the second active region, so thatvariations in the second refractive index modulate a phase of the lightin the second waveguide and vary an optical path length traversed by thelight in the second waveguide, and a second absorption in the secondactive region, so that variations in the second absorption modulate anintensity of the light in the second waveguide; dissipating heat fromthe control circuitry with a heat sink; and thermally isolating thefirst active region, the second active region, and the heater from theheat sink.
 9. The method of claim 8, further comprising providing aselectable current to the heater to set a temperature at the firstactive region to a first specified value and set a temperature at thesecond active region to a second specified value.
 10. The method ofclaim 8, further comprising: with the heater, varying the firstabsorption in the first active region, so that variations in the firstabsorption modulate an intensity of the light in the waveguide, and sothat the heater, the first active region, and the second active regionfunction as at least part of an electro-absorption modulator.
 11. Themethod of claim 8, further comprising: with the heater, varying thefirst refractive index in the first active region, so that variations inthe first refractive index modulate a phase of the light in the firstwaveguide, so that the heater and the first active region function as atleast part of a first electro-optic modulator; with the heater, varyingthe second refractive index in the second active region, so thatvariations in the second refractive index modulate a phase of the lightin the second waveguide, so that the heater and the second active regionfunction as at least part of a second electro-optic modulator; andarranging the first and second electro-optical modulators in a push-pullconfiguration to form a Mach-Zehnder modulator.
 12. The method of claim8, further comprising producing electric fields in the first and secondactive regions with a plurality of electrodes, the electric fields beingdependent on selectable voltages.
 13. The method of claim 12, furthercomprising providing the selectable voltages to the plurality ofelectrodes with the control circuitry.
 14. The method of claim 13,wherein the control circuitry is configured to provide the selectablevoltages to the plurality of electrodes in response to a detectedwavelength change in the light directed through the first or secondactive regions, the selectable voltages being selected to stabilize aphase or an intensity of the light directed through the first or secondactive regions.
 15. A method for modulating light, the methodcomprising: guiding light through a first active region of a firstwaveguide and a second active region of a second waveguide; producingelectric fields in the first and second active regions with a pluralityof electrodes controlled by control circuitry, the electric fields beingdependent on a selectable voltage; selectively heating the first andsecond active regions with a single heater positioned alongside andbetween the first and second active regions and controlled by thecontrol circuitry, wherein operatively the electric field and heatervary at least one of: a first refractive index in the first activeregion, so that variations in the first refractive index modulate aphase of the light in the first waveguide and vary an optical pathlength traversed by the light in the first waveguide, and a firstabsorption in the first active region, so that variations in the firstabsorption modulate an intensity of the light in the first waveguide;wherein operatively the heater further varies at least one of: a secondrefractive index in the second active region, so that variations in thesecond refractive index modulate a phase of the light in the secondwaveguide and vary an optical path length traversed by the light in thesecond waveguide, and a second absorption in the second active region,so that variations in the second absorption modulate an intensity of thelight in the second waveguide; dissipating heat from the controlcircuitry with a heat sink; and thermally isolating the first activeregion, the second active region, and the heater from the heat sink. 16.The method of claim 15, further comprising: with the electric field andthe heater, varying the first absorption in the first active region, sothat variations in the first absorption modulate an intensity of thelight in the first waveguide, and so that the modulating systemfunctions as an electro-absorption modulator.
 17. The method of claim15, further comprising: with the electric field and the heater, varyingthe first refractive index in the first active region, so thatvariations in the first refractive index modulate a phase of the lightin the first waveguide, so that the heater and the first active regionfunction as at least part of a first electro-optic modulator; with theelectric field and the heater, varying the second refractive index inthe second active region, so that variations in the second refractiveindex modulate a phase of the light in the second waveguide, so that theheater and the second active region function as at least part of asecond electro-optic modulator; and arranging the first and secondelectro-optical modulators in a push-pull configuration to form aMach-Zehnder modulator.